The focal point along the passive axis is fix and usually different from the one on the active axis.
- The width of the beam is along the active axis and the length along the passive axis
- In the first part, the length and width of the beam are getting smaller
- In the second part, the passive focal zone, the length remain the same but the width continues to get smaller
- In the third part, the length grows and the width continues to get smaller
- In the fourth part, the active focal zone, the length continues to grow and the width remains the same
- Finally in the fifth part, both length and width grow
When using a 2-D probe, the distance of the focal point can be changed along both axis.